1. Field of the Invention
This invention relates to flat panel devices such as a flat cathode ray tube (CRT) display. More particularly, this invention relates to a support structure for internally supporting a faceplate and backplate of a flat panel device and, most particularly, to such a support structure that resists electrostatic charging.
2. Related Art
Numerous attempts have been made in recent years to construct a flat CRT display (also known as a "flat panel display") to replace the conventional deflected-beam CRT display in order to provide a lighter and less bulky display. In addition to flat CRT displays, other flat panel displays, such as plasma displays, have also been developed.
In flat panel displays, a faceplate, a backplate, and connecting walls around the periphery of the faceplate and backplate form an enclosure. In some flat panel displays, the enclosure is held at vacuum pressure, e.g., in flat CRT displays, approximately 1.times.10.sup.-7 torr. The interior surface of the faceplate is coated with light emissive elements such as phosphor or phosphor patterns which define the active region of the display. The light emissive elements are caused to emit light, e.g., cathodic elements located adjacent the backplate are excited to release electrons which are accelerated toward the phosphor on the faceplate, causing the phosphor to emit light which is seen by a viewer at the exterior surface of the faceplate (the "viewing surface").
In vacuum pressure flat panel displays, a force is exerted on the walls of the flat panel display due to the differential pressure between the internal vacuum pressure and the external atmospheric pressure that, left unopposed, can make the flat panel display collapse. In rectangular displays having greater than an approximately 1 inch diagonal (the diagonal is the distance between opposite corners of the active region), the faceplate and backplate are particularly susceptible to this type of mechanical failure due to their high aspect ratio. Here, "aspect ratio" is defined as either the width, i.e., distance between the interior surfaces of opposing connecting walls, or the height, i.e., distance between the interior surface of the faceplate and the interior surface of the backplate, divided by the thickness. The faceplate or backplate of a flat panel display may also fail due to external forces resulting from impacts sustained by the flat panel display.
Spacers have been used to internally support the faceplate and/or backplate. Previous spacers have been walls or posts located between pixels (phosphor regions that define the smallest individual picture element of the display) in the active region of the display.
Spacers have been formed by photopatterning polyimide. However, polyimide spacers have been found inadequate because of: 1) insufficient strength; 2) inability to match the coefficient of thermal expansion with the materials typically used for the faceplate (e.g., glass), backplate (e.g., glass, ceramic, glass-ceramic or metal) and addressing grid (e.g., glass-ceramic or ceramic), resulting in registration problems; and 3) outgassing that may occur when polyimide is used in a vacuum pressure environment.
Spacers have also been made of glass. However, glass may not have adequate strength. Further, micro-cracks that are inherent in glass make glass spacers even weaker than "ideal" glass because of the tendency of micro-cracks to propagate easily throughout glass.
Additionally, for any spacer material, the presence of the spacers may adversely affect the flow of electrons toward the faceplate in the vicinity of the spacer. For example, stray electrons may electrostatically charge the surface of the spacer, changing the voltage distribution near the spacer from the desired distribution and resulting in distortion of the electron flow, thereby causing distortions in the image produced by the display.